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No. 489,461. Patented Jan. 10, 1893.

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PARKER C. OHOATE, OF NEW YORK, N. Y.

ART F PRODUCING M ETALLIC ZINC.

SPECIFICATION forming part of Letters Patent No. 489,461, dated January 10, 1893.

Application filed July 1, 1892. Serial No. 438,646. (No specimens.)

T0 aZZ whom it may concern-.-

Be it known that I, PARKER O. CHOATE, a citizen of the United States, residing in the city of New York, in the county and State of New York, have invented certain new and useful Improvements inthe Art of Producing Metallic Zinc, (Case No. 8,) of which the following is a specification.

My invention relates to the production of metallic zinc from its ores and the objectof my improvements is to provide an economical method of producing a commercial brand of spelter substantially free from impurities.

While my process may be used in producing metallic zinc from any of its ores, it is more particularly intended to be used in connection with an ore carrying both lead and zinc and is especially valuable as applied to that large class of ores known as complex or blendous galena which carry zinc, iron, sulphur, lead, gold, silver, copper and gangue matter and usually also varying percentages of other metals such as antimony, cadmium, selenium, arsenic, bismuth,'&c. and which on account of the difficulty of working them economically have heretofore been discarded at the mines in great quantities as waste products. In working such ores by the processes heretofore employed, there has been a total loss of zinc, except where utilized as a pigment, and all attempts to produce a commercial brand of metallic zinc therefrom, even at the expense of sacrificing the other constituents of value, have resulted in failure.

As is well known to the art, zinc of commerce has heretofore been produced only by distilling it directly from the ore in retorts or muffles, the ore when necessary being desulphurized prior to distillation.

In all the processes of distillation heretofore employed, very considerable percentages of the other metals associated with the zinc in the ore appear in the zinc product. Thus such metals as iron, copper, &c. which are charged into the retort or muffle with the zinc ore, although not volatile, will always be found in the distilled zinc. The more volatile constituents of zinc ores such as sulphur, arsenic, antimony, cadmium, &c. are to a certain extent driven ofi by the desulphurizing roast above referred to. They cannot, however, be wholly removed by any roasting treatment of the body of the ore, but when/present in the ore will always appear in the distilled product. For these reasons distillation as a method of producing metallic zinc has not heretofore been applicable to the impure blendous ores of zinc, but has only been employed to treat ores rich in zinc, and comparatively free from impurities. Even as produced from such ores by distillation zinc of commerce is universally impure, the nature and amount of the impurities being dependent upon the character of the ore.

Another serious trouble heretofore met with in treating the body of an ore directly in retorts or muffles is that the metallic oxides present in zinc ores form fusible slags with the body of the retort or muffle at the high degree of heat required for distillation, and thus soon destroy the vessel, involving heavy loss and expense. An attempt has been made to remedy this by volatilizing the zinc before distillation leaving behind in the furnace the gangue or earthy matter contained in the ore and charging the muffle or retort with the volatilized and condensed product or fume. On account however of the difficulty of distilling the soft, flocculent product and because of the large quantity of blue powder or oxidized zinc, which it was found resulted from the use of volatilized zinc product in the retorts, this method has never been practically employed. I have found however that by heating the zinc fume in the presence of lead either in the shape of lead fume or finely pulverized metallic lead, the mass becomes condensed and granulated, so that it more nearly resembles in its physical characteristics a crushed ore,whereby its rapid and even distillation is renderedentireiy practicable and the formation of the blue powder is to a great extent prevented.

To the end therefore of producing a commercial brand of zinc from the most complex zinc ores in an economical manner my invention consists in separating the zinc from the less readily volatile constituents of the ore by heating the ore in the presence of a reducing agent to decompose it and reduce the zinc compounds, volatilizing the zinc and other readily volatilizable constituents of the ore and leaving the other constituents behind in the furnace and condensing and collecting the volatilized products in the shape of fume, then heating the Zinc fume in the presence of lead or lead fume and finally reducing and distilling it and separating the resulting molten lead from the zinc.

The accompanying drawing shows a sectional elevation of a form of muffle or retort which may be used with advantage in the distilling part of the process.

By preference I apply my process to ores carrying together with zinc such an amount of lead that it will enter the volatilized zinc fume to the extent of at least five per cent. of such product.

In carrying my invention into effect as applied to such ores, the ore should be first crushed and then, when it contains an excess of sulphur, it may be subjected to the ordi nary desulphurizing roast. The ore is then mixed with carbonaceous fuel such as coal screenings and roasted in any well known type of furnace in which air is admitted underneath the grate at a temperature sufficiently high to volatilize the zinc until the zinc contents of the ore are driven off. \Vith the zinc will also pass off the'lead and the more volatile constituents such as arsenic, cadmium the. The volatilized zinc and other volatilized bodies are then caught and collected in a bag room in the ordinary manner in the shape of fume. The non-volatile matter will be left behind in the furnace and will carry all the copper and gold and most of the silver contained in the ore, and the whole mass will be left in an oxidized and semi-fused condition highly suitable for-smelting, whereby the above mentioned metals may be saved. The object of this first step is three-fold, since it separates the zinc from the metallic oxides which would destroy the retorts, enables the copper, silver and gold to be saved, and yields a mixed zinc and lead fume from which all metallic compounds more volatile than zinc such as cadmium, arsenic, antimony, the. can be separated leaving the zinc and lead fumes together. The collected fume which will be in a very soft, flocculent form may then be reheated in any suitable form of muii'le furnace at a temperature of from 300 to S00 Fahrenheit or sufficient to drive off the compounds more volatile than zinc, care being taken not to revolatilize any of the zinc or lead contents. The mass should preferably be agitated while heating, in order that it may all receive the required degree of heat. As a result of this roast the mass will be freed from the metals more volatile than zinc such as antimony, arsenic, cadmium, the. only the zinc and lead fume being left. In case this roast is employed the desired change in the physical character of the zinc fume will be partially effected therein, being completed afterward in the distilling roast. If however it is not deemed necessary to eliminate from the fume the more volatile constituents above mentioned this roast may be omitted and the effect of granulating and condensiug the mass of zinc fume by the melting of the lead present will be accomplished in the distilling roast which follows, before distillation begins.

The next step in the process is the reduction of the zinc fume to metallic form by distillation. For this purpose the mixed zinc and lead fume, preferably slightly moistened, is mixed with carbon in the form of crushed coal and charged into a retort or muffle, which may be of the form shown in the drawing at A. It is placed upright in the furnace and is provided with an inner perforated tube B having an opening D at the bottom. The retort having been compactly filled with fume and the cover 0 luted on, heat is applied and when a temperature sufficient to volatilize the zinc fume is reached, a current of gas and zinc vapor is established passing through the perforations in the tube B and down the interior of the tube. The gas will pass off as such while the zinc vapor condenses into molten zinc at the mouth of the tube and is caught in a suitable vessel underneath. The lead as reduced melts and trickles down the inside of the tube B with the zinc and is caught in the same vessel underneath. The process of reduction is facilitated by placing a stick of carbon, or of wood which will carbonize, in the central flue B which will clear the reduced zinc and lead of any oxidized film. The presence of the lead in the retort not only operates to facilitate the distillation of the zinc fume by granulating and condensing it but also assistsin preventing the formation of an undue proportion of blue powder. It seems to act as a nucleus and to liquefy and amalgamate with itself such powder of zinc as may be formed, which would otherwise become condensed in a pulverulent nonliquid form and which as is well known resists all attempts to melt and reduce it to liquid form. The mixed zinc and lead is allowed to stand in a suitable vessel, being kept in the molten state, until the lead settles out by gravity, when the lead may be drawn off by means of a cock at the bottom of the vessel, and the zinc may be dipped or run off from the top. The zinc cannot be entirely freed from lead by this process since it will dissolve and carry a percentage of the lead varying in amount from one and one-fourth to one and three-fourths per cent. of the zinc. If the process be carefully carried out and the tools and vessels used are not allowed to contaminate the molten product, this percentage of lead will be the only impurity contained in the zinc.

While I prefer to apply my invention to those ores of zinc of which lead is a constituent, it will be evident that it may, if desired, be applied to zinc ores not containing lead by mixing lead fume or pulverized metallic lead with the zinc fume before distilling it, the proportion of lead or lead fume being not less than five per cent. of the zinc fume.

Instead of the use of the volatilized product collected in the bag-room for subsequent purification and distillation, I may also use the so-called flue dust incident to the manufacture of a zinc-lead fume, which may carry, besides the zinc and lead and the more volatile impurities, from three to five per cent. of iron oxide or silica, mechanically carried over from the furnace. This is non-volatile and in the process of distilling will remain with the coal ash in the retort and not appreciably afiect the purity of the distilled zinc.

While I prefer the form of retort shown herein both because it is more durable on account of its position in the furnace, and because its use assists in preventing the formation of blue powder by bringing the melted lead into intimate contact with the zinc fume and zinc vapor, I do not limit myself to any particular form of apparatus but might use for example, a retort inclined in the furnace so that the molten lead can be drawn off at the lower end of the retort while the zinc vapor passes out of a nozzle at the upper end.

The advantages of my invention will be readily apparent to those skilled in the art, since it prevents the formation of fusible slags within the body of the retort in the dis tillation of zinc, and provides an economical method of producing from impure ores of zinc a commercial metallic zinc carrying lead as its only impurity. While such a brand of zinc is applicable to numerous purposes, its most advantageous use will be in the desilverizing of lead bullion as universally practiced. It may also be refined to great purity by means of the electric current, which is not the case with brands of zinc carrying cadmium, copper, tin, &c.

I am aware that metallic zinc has heretofore been produced from ores of zinc containing lead by distillation directly from the ore, and also that attempts have heretofore been made to distill zinc from a zinc fume free from lead, and I do not broadly claim such processes. I am not aware however that the use of lead or lead fume to render practicable the distillation of zinc fume has ever been practiced or known prior to my invention.

Having thus described my invention, What I claim as new and desire to secure by Letters Patent is:

1. The hereinbefore described process of producing metallic zinc which consists in heating an ore of zinc carrying lead, in the presence of a reducing agent, in a furnace to which air is admitted, so as to volatilize the zinc and lead and those constituents of the ore more volatile than zinc, thereby obtaining a mixed zinc and lead fume free from the less volatile constituents of the ore; heating the mixed fume to drive oif the constituents more volatile than zinc, and granulate and condense the mass; heating the product mixed with carbon in a retort to distill the zinc and finally condensing the zinc vapor and drawing off the molten lead and metallic zinc substantially as set forth.

2. The hereinbefore described process of producing metallic zinc which consists in heating zinc fume mixed with lead fume or pulverized metallic lead, to granulate and condense the fume, heating the product mixed with carbon in a retort to distill the zinc, and finally condensing the zinc vapors and separating the metallic zinc and molten lead, substantially as set forth.

In testimony whereof I have hereunto subscribed my name this 30th day of June, A.

PARKER O. OHOATE. Witnesses:

GERTRUDE P. W001), OLARKsoN A. OoLLINs. 

